Microstructural mechanisms of fatigue crack non-propagation in TRIP-maraging steels

In contrast to conventional martensitic steels, transformation-induced plasticity (TRIP)-maraging steels exhibit exceptional high ductility without sacrificing strength and excellent fatigue property owing to the retained austenite/maraging martensite laminated structure. In this study, TRIP-maraging steel (Fe-9Mn-3Ni-1.4Al-0.01C, wt.%) with fine grained austenite was used to investigate the mechanism of high cycle fatigue resistance. Our analyses revealed that soft austenite region acts as a preferential crack propagation path, but the plastic deformation during crack opening involves martensitic transformation, resisting subsequent crack growth via transformation-induced local hardening or crack closure. Moreover, crack growth along the laminates and across the block boundary forms a zigzag crack path, which would act as roughness-induced crack closure. The combined effect of these factors plays an important role in resisting fatigue crack growth at high cycle fatigue.